This invention relates to error recovery at the moving picture transmission time in a network where an error is not negligible.
Hitherto, a method wherein a moving picture transmission apparatus provides redundant data for error recovery and when an error occurs in a moving picture reception apparatus, the redundant data is used to recover from the error has been known as an error recovery method applied when moving picture data stored in the moving picture transmission apparatus is transferred to the moving picture reception apparatus over a transmission line.
Generally, moving picture data can be assumed to consist of a plurality of still images successive in time sequence. In an MPEG image compression technique, the moving picture data consists of I picture (intraframe coded image), P picture (interframe forward predictive coded image), and B picture (bidirectional predictive coded image), and redundancy in the time direction of the moving picture data is reduced. To enable a random jump, an I picture appears periodically. Such a structure is useful for a system such as a VOD (video on demand) system.
FIG. 10 shows an example of a system using an error recovery method in moving picture transmission in a related art. A moving picture transmission apparatus 1001 comprises network interface means 1004, data transmission means 1005, data reception means 1006, moving picture supply means 1007 for supplying a moving picture, moving picture data acquisition means 1008 for acquiring object data, and redundant data addition means 1016 for adding redundant data. A moving picture reception apparatus 1002 comprises network interface means 1009, data transmission means 1011, data reception means 1012, input means 1010 for making a request for the reproduction state of a moving picture, error determination means 1013 for determining an error, decoding means 1014 for decoding moving picture data into a format in which the moving picture data can be displayed, and display means 1015 for displaying a moving picture.
In the system, when the user enters a command through the input means 1010 of the moving picture reception apparatus 1002, the command is sent through the data transmission means 1011, the network interface means 1009, a transmission line 1003, the network interface 1004 of the moving picture transmission apparatus 1001, and the data reception means 1006 to the moving picture data acquisition means 1008, which then acquires objective moving picture data from the moving picture supply means 1007 in accordance with the command. The redundant data addition means 1016 adds redundant data to the acquired moving picture data so as to send all frames or I pictures doubly. Then, the resultant data is sent through the data transmission means 1005, the network interface means 1004, the transmission line 1003, the network interface means 1009 of the moving picture reception apparatus 1002, and the data reception means 1012 to the error determination means 1013 for detecting an error during the transmission of the data. If an error does not occur, the error determination means 1013 sends the moving picture data to the decoding means 1014 and the redundant moving picture data is discarded. If an error occurs, the redundant data is sent to the decoding means 1014. The decoding means 1014 decodes the coded moving picture data into displayable form and sends the provided data to the display means 1015, which then displays a moving picture based on the data.
To use the system to add redundant data so as to send all frames doubly, the transmitted data amount is doubled; to add redundant data so as to send I pictures doubly, the transmitted data amount result in about a 1xc2xd-times amount because the I picture occupation percentage between one I picture and the next I picture is about a half.
To transmit a moving picture on a narrow-band transmission line in the error recovery method in moving picture transmission in the related art, the effective band is furthermore narrowed because of the redundant data and the moving picture quality and the frame rate are lowered; this is a problem.
It is therefore an object of the invention to enable error recovery using additional data with smaller redundancy in order to use a band of a transmission line efficiently in an error recovery method in moving picture transmission.
To the end, according to the invention, first, a moving picture data structure wherein a Pxe2x80x2 picture of a forward predictive coded image of a picture immediately preceding an I picture (intraframe coded image) and the I picture is placed preceding or following the I picture is provided.
Thus, if an error occurs in the I picture during the data transmission, the Pxe2x80x2 picture can be used to recover the I picture from the error.
Second, a moving picture data structure wherein a Pxe2x80x3 picture of a forward predictive coded image of an I picture immediately preceding the current I picture and the current I picture is placed preceding or following the current I picture is provided.
Thus, if an error occurs in the I picture or the picture immediately preceding the I picture during the data transmission, the immediately preceding I picture and the Pxe2x80x3 picture can be used to recover the I picture from the error.
Third, a moving picture transmission apparatus comprises differential data transmission means for transmitting data for error correction on a different band when moving picture data is transmitted to a transmission line.
Thus, differential data can be transmitted without hanging data transmission means.
Fourth, a moving picture transmission apparatus comprises time information addition means for adding the same time information as moving picture data to data for error correction when the moving picture data is transmitted to a transmission line.
Thus, the moving picture data reception apparatus receiving the moving picture data can separate the received data into the moving picture data and the data for error correction.
Fifth, a moving picture transmission apparatus comprises redundancy control data reception means for receiving redundancy control data from moving picture reception apparatus when the moving picture data is transmitted to a transmission line.
Thus, data for error correction can be optimized for transmission.
Sixth, a moving picture reception apparatus comprises differential data reception means for receiving data for error correction on a different band when moving picture data is received from a transmission line.
Thus, differential data can be received without changing data reception means.